Walsh code management in a code division multiple access cellular wireless communication system

ABSTRACT

A cellular wireless communication system and method of operation manages Walsh codes in order to ensure that sufficient Walsh codes are available to prevent call blocking and to support additional hand-off operations. In an initial operating condition, the cellular wireless communication system services normal hand-off operations in which a maximum number of cells and sectors may participate in hand-off. With hand-off operations according to the present invention, each cell or sector participating in hand-off for a mobile terminal uses a unique Walsh code for covering its forward link signals. When the number of Walsh codes available for servicing new calls is reduced so that it meets or exceeds a Walsh code availability threshold, the number of cells and sectors that may participate in hand-off is reduced from the maximum number. In the number of participating cells/sectors results in release or non-use of some Walsh codes. In subsequent operations when sufficient Walsh codes are available for servicing hand-off operations, a greater number, up to the maximum number of cells and sectors may again participate in hand-off of the mobile terminal.

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §120, as a continuation, to the following U.S. Utility PatentApplication which is hereby incorporated herein by reference in itsentirety and made part of the present U.S. Utility Patent Applicationfor all purposes:

1. U.S. Utility application Ser. No. 10/035,846, entitled “WALSH CODEMANAGEMENT IN A CODE DIVISION MULTIPLE ACCESS CELLULAR WIRELESSCOMMUNICATION SYSTEM,” filed Dec. 24, 2001, pending.

SPECIFICATION Background

1. Technical Field

The present invention relates generally to wireless communications; andmore particularly to Code Division Multiple Access (CDMA) cellularwireless communication systems.

2. Related Art

Cellular wireless communication systems are well known. In a cellularwireless communication system a plurality of base stations providewireless coverage within respective cells that includes respectivepluralities of sectors. In aggregation, the base stations work togetherto support wireless communications within a service area. The basestations are coupled via at least one Base Station Controller (BSC) to amobile switching center (MSC). The MSC couples to the Public SwitchedTelephone Network (PSTN) and services voice traffic for all servicedmobile terminals. For the service of packetized communication, e.g.,between mobile terminals and the Internet, a packet data link betweenthe BSC and one or more packet data networks is provided.

Various cellular operating standards exist. These cellular standardsinclude, for example, the Advanced Mobile Phone System (AMPS) standards,the Narrowband Advanced Mobile Phone Service (NAMPS) standards, theGlobal Standards for Mobile Communications (GSM) standards, the CodeDivision Multiple Access (CDMA) standards, and the Time DivisionMultiple Access (TDMA) standards among others. These cellular standardsare continually improved and updated to service ever increasing cellularwireless communication system demands. Currently, various CDMA systemsare deployed, e.g., IS-95A and IS-95B, and additional CDMA systems areplanned for deployment, e.g., 1xRTT, 1xEV-DO, etc.

CDMA systems are direct sequence spread spectrum systems in which aplurality of spread-spectrum signals are transmitted simultaneously inthe same frequency band, both on forward links from base stations tomobile terminals and on reverse links from the mobile terminals to thebase stations. Each intended mobile terminal is assigned at least onedistinct Walsh code that identifies the signals sent to, or receivedfrom mobile terminal. Of a plurality of forward link spread-spectrumsignals intended for a respective plurality of mobile terminals, each iscovered by a respective Walsh code. For example, forward link signalsintended for a first mobile terminal are covered by a first Walsh code,g₁(t), and forward link signals intended for a second mobile terminalare covered by a second Walsh code, g₂(t), etc. Each mobile terminalreceives a composite spread spectrum signals within the shared frequencyband at its antenna, such composite signal including energy intended forall serviced mobile terminals. However, after despreading the receivedsignal with its assigned Walsh code, the receiver of the mobile terminaloutputs all the energy of its intended signal but only a small fractionof the energy of signals intended for other mobile terminals. Thus, thesignals intended for the mobile terminal may be extracted from thereceived composite signal by using the assigned Walsh code.

CDMA capacity is interference limited. The number of mobile terminalsthat may be supported within a particular area is determined by thetotal interference power that all of the mobile terminals, taken as awhole, generate. The number of mobile terminals that may be supported byeach base station is limited because the base station can provide only amaximum power output within its respective cell or sectors that must bedivided among the mobile terminals operating within the respective cellor sectors. Thus, as the number of mobile terminals operating within acell increases, the additional amount of power available for new mobileterminals decreases until a minimal level is reached and a maximumnumber of users have been reached for the cell or sector. Dividing thepower in such a fashion sometimes results in dropped calls due to thesignal strength going below a required threshold.

To minimize the dropped call probability and to improve call quality, amobile terminal typically receives forward link signals from more thanone base station and/or from more than one sector of a particular basestation, particularly when the mobile terminal is moving from sector tocell or sector to cell. A “rake receiver” of the mobile terminalreceives and decodes a plurality of forward link signals and thus canreceive and decode these multiple forward link signals. An operationduring which a mobile terminal is moving between cells and sectors iscommonly referred to as “hand-off.” Hand-off between base stations isgenerally referred to as “soft hand-off” while hand-off between sectorsof a single base station is generally referred to as “softer hand-off.”Mobile terminals continually measure the strength of pilot signalsreceived from cells and/or sectors and report these measurements to thewireless network via a servicing base station. Based upon the reportedstrengths of these pilot signals, the wireless network then initiates,services, and terminates forward link signals in respectivecells/sectors based upon the measurements.

Note however, that a mobile terminal that is stationary will typicallyalso receive forward link transmissions from a plurality of cells and/orsectors even though in some cases a single forward link will service acorresponding mobile terminal. Multiple forward link transmissions to asingle mobile terminal may be established even when the mobile terminalinitially receives service. During call setup, the wireless networkinfrastructure typically determines a sector that initially services themobile terminal. Then, resources are allocated within the base stationthat services a corresponding forward link and forward linktransmissions are initiated within the sector (or cell).

An initially servicing forward link is typically the strongest forwardlink and is referred to as the “primary” forward link. Weaker forwardlinks that may be enabled during hand-off are typically referred to as“secondary” forward links. When multiple forward links are operational,a serviced mobile terminal obeys directives from the primary forwardlink, e.g., reverse link power control directives.

In newer CDMA systems, improved Coder DECoder (CODEC) technologies allowvoice communications to be supported at lower data rates. Further,improvements in physical layer modulation schemes, Forward Error Coding,and other operations also support lower data rate operations. Because ofthese technological increases, a greater number of users may besupported within each cell/sector before CDMA interference limitationsare reached. For example, in systems using Enhanced Variable Rate CODEC(EVRC) operations, on average, up to 24 users per sector may besupported on each carrier. Further, in 1xRTT systems, on average, up to30 users per sector may be supported on each carrier.

In a typical IS-95A or IS-95B system, 64 Walsh codes are available foruse but at least three Walsh codes are dedicated for use with overheadchannels. In IS-2000 systems either 64 or 128 Walsh codes are available,depending upon the implementation, with some of these also dedicated tooverhead channels. During operation in which an average of 24 users issupported and with which each user is in hand-off with in average of 2.5sectors a total of 64 Walsh codes would be required. This operationalexample would fully deplete the available Walsh codes if 64 Walsh codeswere available. When all Walsh codes are used for servicing calls for aset of mobile terminals, new call setup and new hand-offs are blocked.

Thus, there exits a need in the art for a cellular wirelesscommunication system having improved performance during hand-off andcall setup.

SUMMARY

In order to overcome the above-described shortcomings, as well as othershortcomings of the prior systems and operations, a cellular wirelesscommunication system constructed and operating according to the presentinvention manages Walsh codes in order to ensure that sufficient Walshcodes are available to prevent call blocking and to support additionalcritical hand-off operations. In an initial operating condition, thecellular wireless communication system services normal hand-offoperations in which a maximum number of cells and sectors may provideforward link transmissions. With the operations of the presentinvention, each cell or sector participating in hand-off for a mobileterminal uses a unique Walsh code for covering its forward link signals.

However, during some points in operation, the number of available Walshcodes will be reduced until a Walsh code availability threshold is met,i.e., the number of available Walsh codes is less than the Walsh codeavailability threshold. When this occurs, the number of forward linktransmissions that may be used for each hand-off is reduced from themaximum number to a lesser number, e.g., four or five. A forcedreduction in the number of links per call results in the release ornon-use of some Walsh codes. In subsequent operations when sufficientWalsh codes are available for servicing hand-offs, a greater number ofcells and sectors may again participate in hand-off for each servicedmobile terminal. Note that some cells/sectors may reach a Walsh codeavailability threshold while others have not. In such case, hand-offoperations are limited in some cells/sectors but not in othercells/sectors.

In a particular operation according to the present invention, basestations (and Base Station Transceiving Subsystems “BTSs” locatedtherein) and Base station Controllers (BSCs) operate according to thepresent invention to limit the number of participating cells/sectorsduring hand-off. During normal operations, up to six-way hand-off issupported. When the number of available Walsh codes reaches a Walsh codeavailability threshold, six-way hand-off is precluded. In such case, forany six-way hand-offs, a weakest forward link of the six-way hand-off isterminated and the corresponding Walsh code is released. In a similaroperation, both five-way and six-way hand-off operations are terminated.Thus, when six-way and five-way hand-off operations are precluded atmost four-way handoff is allowed.

With a cellular wireless communication system servicing EnhancedVariable Rate CODEC (EVRC) and other relatively lower data rateoperations, the present invention yields significant benefits. Bylimiting hand-off operations to ensure the availability of Walsh codes,call blocking is minimized or reduced and critical hand-off operationsmay be serviced. Further, because only the weakest links are eliminated,little benefit is lost. Such is the case because the mobile terminalstypically only receive and decode the three strongest forward linksignals. Thus, the weaker links provide no significant benefit. Otheraspects of the present invention will become apparent with furtherreference to the drawings and specification that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present invention can be obtained when thefollowing detailed description is considered in conjunction with thefollowing drawings, in which:

FIG. 1 is a system diagram illustrating a cellular wirelesscommunication system in which Walsh code allocation and use isdynamically managed according to the present invention;

FIG. 2 is a diagram illustrating operations according to the presentinvention in managing Walsh code allocation and use;

FIG. 3 is a diagram illustrating in more detail operations according tothe present invention in managing Walsh code allocation and use;

FIG. 4 is a block diagram illustrating a Base Station TransceivingSubsystem constructed according to the present invention; and

FIG. 5 is a block diagram illustrating a Base Station Controllerconstructed according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system diagram illustrating a cellular wirelesscommunication system 100 in which Walsh code allocation and use isdynamically managed according to the present invention. The cellularwireless communication system 100 includes a mobile switching center(MSC) 102, Base Station Controllers (BSCs) 104 and 106, and a pluralityof base stations 108, 110, 112, and 114 coupled to the MSC 102 viarespective BSCs. Together, these components are referred to as the“wireless network.” Each of the base stations 108 through 114 provideswireless coverage within a plurality of sectors that make up respectivecells. For example, base station 108 provides wireless coverage withinthree sectors (sectors A, B, and C) of cell 120, each of which spans 120angular degrees about base station 108. Base stations 110, 112, and 114provide wireless coverage within cells 122, 124, and 126, each having arespective set of three sectors.

The public switched telephone network 116 (PSTN) couples to MSC 102.With the base stations 108 through 114 providing wireless communicationswithin the service area, a mobile terminal (shown at positions 130, 132,134, and 136) may establish a call with a telephone 118 connected to thePSTN 116 or with other wireless mobile terminals operating within thisor another service area. While the present invention is described withreference to a single mobile terminal and with voice service, theteachings of the present invention apply equally well to data operationsand with multiple mobile terminals.

The mobile terminal initiates a phone call while at position 130 andmoves in from position 130 to positions 132, 134, and 136, in order. Atposition 130 within sector C of cell 120, serviced by base station 108,the mobile terminal initiates a call to telephone 118. The wirelessnetwork receives a call setup request from the mobile terminal andallocates forward link and reverse link resources for servicing the callin a corresponding sector. Upon call completion, the cellular wirelesscommunication system 100 services the call between the mobile terminaland telephone 118 using a path that includes a wireless link between themobile terminal and base station 108, a wired path between base station108 and the PSTN 116 (via BSC 104 and MSC 102), and via the PSTN 116.

In initial call setup and service, the wireless communication systemallocates resources in sector C of cell 120, i.e., the primary link.Thus, a single Walsh code is allocated for the forward link signals frombase station 108 to the mobile terminal at position 130. Note that thepresent invention concerns forward link signals only and the manner inwhich the forward link signals are serviced and managed. Thus, indescribing the present invention, only forward link operations areconsidered and the reader should understand that reverse link operationsare also required for servicing the phone call between the mobileterminal and the telephone 118.

In the described embodiment, the mobile terminal continuously scans forpilot signals transmitted from the base stations 108-114, measures thestrengths of such pilot signals, and upon meeting predeterminedcriteria, reports the strengths and identities of the pilot signals tothe network infrastructure. Information regarding the strength of pilotsignals, as measured by the mobile terminal, is of significance forhand-off operations. Thus, prior to initiating the call, the mobileterminal received pilot signals from the sectors serviced by basestations 108-114, measured the strengths of these pilot signals, andreported the strengths and identities of the pilot signals to thewireless network via a servicing base station, e.g., base station 108.Based upon the pilot signal strengths and identities reported, thewireless network determined that forward link signals should betransmitted only in sector C of cell 120.

When the mobile terminal moves from position to 130 to position 132hand-off operations are performed. During hand-off, the wireless networkcommences transmission of forward link signals within additionalsectors. For example, while moving from position 130 to position 132,base station 108 transmits forward link signals to the mobile terminalin both sectors B and C and base station 110 transmits forward linksignals in both sector A and sector C. This particular operationincludes soft hand-off between cells 120 and 122, softer hand-offbetween sectors C and B of cell 120, and softer hand-off between sectorsA and C of cell 122. This particular hand-off operation is a four-wayhand-off operation because four forward link signals are involved.According to the present invention, each of these forward link signalsis covered by a unique Walsh code. Thus, during this hand-off operation,four unique Walsh codes are used for a single hand-off operation of themobile terminal.

When the mobile terminal moves from position 132 to position 134,sectors B and C of cell 122 and sectors A, B, and C of cell 124participate in the hand-off. This hand-off operation is a five-wayhandoff operation in which five unique Walsh codes are employed. Whenthe mobile terminal moves from position 134 to position 136, sectors A,B, and C of cell 124 and sectors A, B, and C of cell 126 participate inhand-off. This hand-off operation is a six-way handoff operation inwhich six unique Walsh codes are employed.

In an initial operation according to the present invention, up tosix-way hand-off is supported, as required by some operating standards.However, when a number of available Walsh codes compares unfavorably toa threshold, e.g., is less than a Walsh code availability threshold,hand-off operations are limited. In one particular operation accordingto the present invention, when a Walsh code availability threshold ismet, hand-off is limited to at most four-ways.

Thus, five-way and six-way hand-off operations are prohibited. Inprohibiting five-way and six-way hand-off, any mobile terminals that arebeing handed off will not be serviced by more than four forward links.For those mobile terminals participating in five-way or six-way handoff,one or two forward link signals are terminated, respectively. Further,all new hand-offs will be limited to a corresponding number of forwardlinks, i.e., four-way. A determination as to which forward link signalto terminate is based upon the relative strengths of pilot signalscorresponding to the forward links, as reported by the mobile terminal.

In determining which of the forward links to terminate, operationaccording to the present invention may consider the instantaneousstrength of the forward link transmissions, as measured by and lastreported by the mobile terminal. Such reporting of pilot signalstrengths is consistent with standardized hand-off operations. Withthese operations, the mobile terminal has one rake of its multiple rakereceivers constantly scanning active carriers for pilot signals, each ofwhich is distinguished from other pilot signals on a same carrier by aPseudo-Noise (PN) offset of a corresponding PN sequence. When the mobileterminal finds a pilot signal, it measures the strength of the pilotsignal and determines the PN offset of the pilot signal. Then, themobile terminal reports the strengths of the pilot signals and thecorresponding PN offsets in a pilot signal strength measurement message(PSMM). The mobile terminal may send the PSMM periodically, e.g., everysecond, every 2 seconds, etc., or it may send this message when athreshold condition is met, e.g., when the change in relative strengthsof the pilots signals exceeds a threshold. The supporting networkinfrastructure receives the reported pilot signal strengths and PNoffsets from the mobile terminal and allocates/deallocates forward linktransmissions based thereupon.

Thus, the operations of the present invention may be performedconsistently with prior hand-off operations in terminating the weakestor two weakest forward link transmissions based upon the last reportedpilot signal strengths. Such operations would consider the instantaneousstrengths of the pilot signals, as last reported by the mobile terminal.In another operation according to the present invention, the strengthsof the pilot signals are averaged over a time period based upon multiplePSMM reports from the mobile terminal. With these “averaging”operations, temporary perturbations in pilot signal strengths will besmoothed.

With particular reference to FIG. 1, when the mobile terminal is movingfrom position 134 to position 136, it is in six-way hand-off. Duringthis six-way handoff operation, a Walsh code availability threshold ismet and six-way hand-off is prohibited. Based upon the strength of pilotsignals previously reported by the mobile terminal, according to thepresent invention, transmissions in sector A of cell 124 and in sector Bof cell 126 are terminated. After termination, the mobile terminal is infour-way hand-off.

In an alternate operation according to the present invention, the mobileterminal initiates a call to telephone 118 while at position 132. Basedupon reported pilot signal strengths, the cellular wireless networkwould like to initiate five-way hand-off in initially servicing thecall. However, because a Walsh code availability threshold hadpreviously been met, five-way and six-way hand-off are prohibited andonly four-way hand-off is serviced.

FIG. 2 is a diagram illustrating operations according to the presentinvention in managing Walsh code allocation and use. Upon initiation ofoperation according to the present invention, normal hand-off operationsare performed (step 202). With these normal hand-off operations, nolimitation is placed on the number of cells/sectors that can participatein the hand-off of a mobile terminal. As was described with reference toFIG. 1, in one embodiment, six-way hand-off is supported.

In an operation according to the present invention, when a number ofuser terminals increases from a minimal level, Walsh code availabilitywill fall below a Walsh code reserve requirement (step 204). In oneembodiment of a CDMA system that operates according to the presentinvention, sixty-four (64) Walsh codes are available for use in eachsector, with at least three Walsh codes dedicated to overhead channels.Thus, for example, with 22 mobile terminals consuming 52 Walsh codes,and with 3 Walsh codes consumed for overhead channels, a total of 55Walsh codes are used with 9 Walsh codes remaining in reserve. With theWalsh code availability threshold (Walsh code reserve requirement) setto 10 Walsh codes, the number of available Walsh codes has fallen belowthe availability threshold.

With the Walsh code availability threshold met, operation according tothe present invention limits the number of forward links that may beused for hand-off operations (step 206). In one particular operation,five-way and six-way hand-off operations are precluded. For eachcurrently serviced call having being in hand-off with a number offorward links that exceeds a hand-off limit, e.g., five-way or six-wayhandoff, one or more of the weakest forward links for these calls areterminated (step 208). Limited hand-off operations then continue (step210) until the Walsh code reserve requirement is met (step 212). Whenthe Walsh code reserve requirement is met, normal hand-off operationsresume (step 214).

FIG. 3 is a diagram illustrating in more detail operations according tothe present invention in managing Walsh code allocation and use. Inservicing hand-off operations, no limitation initially exists, e.g.,six-way and all lesser hand-off operations are allowed (step 302).However, when a first Walsh code availability threshold limit isexceeded, e.g., 10 remaining available Walsh codes (step 304), six-wayhand-off operations are blocked (step 306). When six-way hand-offoperations are blocked, for those mobile terminals currently beingserviced by six-way hand-off, a weakest forward link of the sixtransmitting sectors/cells is determined (step 308), such forward linksignals are terminated, and the Walsh code used therefore is returned tothe Walsh code pool (step 310). As was previously described, thestrength of the forward links are determined based upon prior pilotsignal strength measurement messages previously received by the cellularwireless network infrastructure from the mobile terminal. From step 310,operation returns to step 302 with hand-off limitations as indicated.

When a second Walsh code availability threshold is exceeded, e.g., 5remaining available Walsh codes step (312), five-way hand-off operationsare blocked (step 314). When five-way hand-off operations are blocked,for those mobile terminals currently being serviced by five-wayhand-off, a weakest forward link of the five transmitting sectors/cellsis determined (step 316), such forward link signals are terminated, andthe Walsh code used therefore is returned to the Walsh code pool (step318). From step 318, operation returns to step 302 with hand-offlimitations set as indicated.

In a typical operation, the Walsh code availability threshold of step304 would first be exceeded. Then, if the operations of steps 306through 310 fail to provide a sufficient number of available Walshcodes, the threshold operations of step 312 may be met. When asufficient number of Walsh codes are available, based upon a thresholdthat is set, e.g., 15 Walsh codes, (at step 320), five-way and six-wayhand-off is then allowed (step 322). From step 322, operation returns tostep 302 with normal hand-off operations allowed.

Note that different cells/sectors may have different operatingconditions. For those cells/sectors that are heavily loaded, no five-wayor six-way operations may be precluded. However, for those cells/sectorsthat are lightly loaded, five-way or six-way operations may be allowed.When some cells are hand-off limited and other cells are not hand-offlimited, the cells-that are hand-off limited will provide weaker forwardlinks even though they will provide primary forward links and strongersecondary links.

FIG. 4 is a block diagram illustrating a Base Station TransceivingSubsystem (BTS) 402 constructed according to the present invention. TheBTS 402 supports an operating protocol that is compatible with theteachings of the present invention, e.g., IS-95A, IS-95B, 1xRTT,1xEV-DO, etc. The BTS 402 includes a processor 404, dynamic RandomAccess Memory (RAM) 406, static RAM 408, Flash memory EPROM 410 and atleast one data storage device 412, such as a hard drive, optical drive,tape drive, etc. These components (which may be contained on aperipheral processing card or module) intercouple via a local bus 417and couple to a peripheral bus 420 (which may be a back plane) via aninterface 418. Various peripheral cards couple to the peripheral bus420. These peripheral cards include a BSC interface card 424, whichcouples the BTS 402 to its servicing BSC.

Sector call processing cards 426, 428, and 430 couple to Radio Frequency(RF) units 432, 434, and 436, respectively. Each of these sector callprocessing cards 426, 428, and 430 performs digital processing for arespective sector, e.g., sector 1, sector 2, or sector 3, serviced bythe BTS 402. The RF units 432, 434, and 436 couple to antennas 442, 444,and 446, respectively, and support wireless communication between theBTS 402 and mobile stations (the structure of which is shown in FIG. 4).The BTS 402 may include other cards 440 as well.

Walsh Code Management Instructions (WCMI) 416 are stored in storage 412.The WCMI 416 are downloaded to the processor 404 and/or the DRAM 406 asWCMI 414 for execution by the processor 404. While the WCMI 416 areshown to reside within storage 412 contained in BTS 402, the WCMI 416may be loaded onto portable media such as magnetic media, optical media,or electronic media. Further, the WCMI 416 may be electronicallytransmitted from one computer to another across a data communicationpath. These embodiments of the WCMI are all within the spirit and scopeof the present invention.

Upon execution of the WCMI 414, the BTS 402 performs operationsaccording to the present invention previously described herein withreference to FIGS. 1-3. The WCMI 416 may also be partially executed bythe digital processing cards 426, 428, and 430 and/or other componentsof the BTS 402. Further, the structure of the BTS 402 illustrated isonly one of many varied BTS structures that could be operated accordingto the teachings of the present invention.

FIG. 5 is a block diagram illustrating a Base Station Controller (BSC)502 constructed according to the present invention. The structure andoperation of BSCs is generally known. The BSC 502 services both circuitswitched and packet switched operations. In some cases, the BSC 502 iscalled upon to convert data between circuit switched and data switchedformats, depending upon the types of equipment coupled to the BSC 502.The components illustrated in FIG. 5, their function, and theinterconnectivity may vary without departing from the teachings of thepresent invention.

The BSC 502 includes a processor 504, dynamic RAM 506, static RAM 508,EPROM 510 and at least one data storage device 512, such as a harddrive, optical drive, tape drive, etc. These components intercouple viaa local bus 517 and couple to a peripheral bus 519 via an interface 518.Various peripheral cards couple to the peripheral bus 519. Theseperipheral cards include an IP network interface card 520, a basestation manager card 524, a selector band subsystem card 528, a MSCinterface card 530, and a plurality of BTS interface cards 534, 538 and542.

The IP network interface card 520 couples the BSC 502 to an IP network522. The base station manager interface card 524 couples the BSC 502 toa Base Station Manager 526. The selector card 528 and MSC interface card530 couple the BSC 502 to the MSC/HLR/VLR 532. the BTS interface cards534, 538, and 542 couple the BSC 502 to base stations served by BaseStation Transceiving Subsystems (BTSs) 536, 540, and 546, respectively.Walsh code management Instructions (WCMI), along with the BSC 502hardware, enable the BSC 502 to perform the operations of the presentinvention. The WCMI 516 are loaded into the storage unit 512 and, upontheir execution, some or all of the WCMI 514 are loaded into theprocessor 504 for execution. During this process, some of the WCMI 516may be loaded into the DRAM 506. In some operations, the selector banksubsystem card 528 executes some or all of the WCMI to implement theteachings of the present invention.

In view of the above detailed description of the present invention andassociated drawings, other modifications and variations will now becomeapparent to those skilled in the art. It should also be apparent thatsuch other modifications and variations may be effected withoutdeparting from the scope of the present invention as set forth in theclaims that follow.

1. A method for managing Walsh Codes in a Code Division Multiple Access(CDMA) cellular wireless communication system, the method comprises:assigning a first plurality of Walsh Codes to the mobile terminal,wherein each of the plurality of assigned Walsh Codes corresponds to acell or sector providing forward link transmissions to the mobileterminal; determining whether an insufficient number of unused WalshCodes is available based upon a first handoff participation limit; andwhen an insufficient number of unused Walsh Codes is available, reducingthe first handoff participation limit to a second handoff participationlimit to produce a reduced handoff participation limit, the secondhandoff participation limit being less than the first handoffparticipation limit, wherein either of the first or the second handoffparticipation limit serve to determine a maximum number of cells orsectors that participate in handoff with any serviced mobile terminal;and when the mobile terminal participates in a handoff with a number ofcells or sectors that exceeds the reduced handoff participation limit,limiting the number of forward link transmissions to the mobile stationfrom a corresponding number of servicing cells or sectors to release acorresponding number of Walsh Codes to come within the reduced handoffparticipation limit.
 2. The method of claim 1, wherein limiting thenumber of cells or sectors providing forward link transmissions to themobile terminal to thereby limit the number of Walsh Codes beingemployed in servicing the mobile terminal comprises terminating at leastone forward link serviced by the number of cells or sectors for themobile terminal.
 3. The method of claim 2, wherein terminating at leastone forward link serviced by the number of cells or sectors for themobile terminal further comprises: determining a weakest forward linkserviced by the cells or sectors for the mobile terminal; andterminating the weakest forward link serviced by the number of cells orsectors for the mobile terminal.
 4. The method of claim 3, wherein theweakest forward link is determined based upon the strength ofcorresponding pilot signals, as measured and reported by the mobileterminal.
 5. The method of claim 4, wherein a plurality of reports ofpilot signal strengths are used in conjunction with averaging operationsto determine the weakest forward link.
 6. The method of claim 1, whereinlimiting the number of cells or sectors providing forward linktransmissions to the mobile terminal to thereby limit the number ofWalsh Codes employed in servicing the mobile terminal further comprises:terminating a weakest forward link when the mobile terminal is infive-way hand-off; and terminating two weakest forward links when themobile terminal is in six-way hand-off.
 7. The method of claim 1,wherein limiting the number of cells or sectors providing forward linktransmissions to the mobile terminal to thereby limit the number ofWalsh Codes being employed in servicing the mobile terminal includesterminating a forward link in a sector that has reached a Walsh codeavailability threshold.
 8. A method for managing Walsh Codes in a CodeDivision Multiple Access (CDMA) cellular wireless communication system,the method comprises: assigning a first plurality of Walsh Codes to eachof a plurality of serviced mobile terminals, wherein each of a pluralityof Walsh Codes servicing a mobile terminal corresponds to respectiveforward link transmissions; determining that an insufficient number ofunused Walsh Codes is available based upon a first handoff participationlimit; and when an insufficient number of unused Walsh Codes isavailable, reducing the first handoff participation limit to a secondhandoff participation limit to produce a reduced handoff participationlimit, the second handoff participation limit being less than the firsthandoff participation limit; and when a mobile terminal of the pluralityof mobile terminals participates in a handoff with a number of cells orsectors that exceeds the reduced handoff participation limit,terminating forward links that are employed for each such mobileterminal of the plurality of mobile terminals to thereby limit thenumber of Walsh Codes being employed to come within the reduced handoffparticipation limit.
 9. The method of claim 8, wherein terminating atleast one forward link for at least some of the plurality of mobileterminal further comprises: for each of the plurality of mobileterminals that are being serviced by a number of forward links thatexceeds a forward link limit, determining a respective weakest forwardlink servicing the mobile terminal; and terminating the respectiveweakest forward link servicing the mobile terminal.
 10. The method ofclaim 9, wherein the respective weakest forward link is determined basedupon the strength of corresponding pilot signals, as measured andreported by the mobile terminal.
 11. The method of claim 10, wherein aplurality of reports of pilot signal strengths are used in conjunctionwith averaging operations to determine the weakest forward link.
 12. Themethod of claim 8, wherein terminating at least one forward linkparticipating for at least some of the plurality of mobile terminalsfurther comprises: terminating a weakest forward link for each mobileterminal being serviced by five forward links; and terminating twoweakest forward links for each mobile unit being serviced by six forwardlinks.
 13. The method of claim 8, wherein a forward link in a sectorthat has reached a Walsh code availability threshold is terminated. 14.A base station controller that supports Code Division Multiple Access(CDMA) operations, the base station controller comprises: a MobileSwitching Center (MSC) interface that interfaces the base stationcontroller to a MSC; at least one base station interface that interfacesthe base station controller to a plurality of base stations; and atleast one digital processor coupled to the base station interface and tothe MSC interface; and a plurality of software instructions that areexecuted by the at least one digital processor that cause the basestation controller to: assign a plurality of Walsh Codes to each of aplurality of serviced mobile terminals, wherein each of a plurality ofWalsh Codes servicing a mobile terminal corresponds to respectiveforward link transmissions; determine whether an insufficient number ofunused Walsh Codes are available based upon a first handoffparticipation limit; and when an insufficient number of unused WalshCodes is available, reduce the first handoff participation limit to asecond handoff participation limit to produce a reduced handoffparticipation limit, the second handoff participation limit being lessthan the first handoff participation limit; and when the mobile terminalparticipates a handoff with a number of cells or sectors that exceedsthe reduced handoff participation limit, terminate at least one forwardlink for at least some of the plurality of mobile terminals and limitingthe number of forward links that are employed for subsequent hand-offs.15. The base station controller of claim 14, wherein in terminating aforward link participating for a mobile terminal, the base stationcontroller determines a respective weakest forward link for the mobileterminal and terminates the respective weakest forward link.
 16. Thebase station controller of claim 15, wherein the base station controllerdetermines the respective weakest forward link based upon the strengthof corresponding pilot signals, as measured and reported by the mobileterminal.
 17. The base station controller of claim 16, wherein aplurality of reports of pilot signal strengths are used in conjunctionwith averaging operations to determine the weakest forward link.
 18. Thebase station controller of claim 14, wherein in terminating at least oneforward link for at least some of the plurality of mobile terminals thebase station controller terminate a weakest forward link for each mobileterminal being serviced by five forward links and terminates two weakestforward links for each mobile unit being serviced by six forward links.19. The base station controller of claim 14, wherein a forward link in asector that has reached a Walsh code availability threshold isterminated.
 20. The base station controller of claim 14, wherein thebase station controller operates consistent with IS-95A, IS-95B, 1xRTT,or 1xEV-DO operating standards.